Use of Eductor for Liquid Disposal from Vessel

ABSTRACT

A system for the processing of a hydrocarbon flare gas. An input gas stream contains a gas component and a liquid component. A knock-out drum separates the gas component from the liquid component. An eductor has a motive inlet, a suction inlet, and a discharge outlet. The separated liquid component is introduced into the suction inlet of the eductor. A high-pressure gas stream is introduced into the motive inlet of the eductor. The high-pressure gas stream has a pressure sufficient to draw the separated liquid component from the knock-out drum and through the discharge outlet.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of both U.S. Provisional PatentApplication No. 62/422,690, filed Nov. 16, 2016 entitled USE OF EDUCTORFOR LIQUID DISPOSAL FROM VESSEL and U.S. Provisional Patent ApplicationNo. 62/262,629, filed Dec. 3, 2015 entitled USE OF EDUCTOR FOR LIQUIDDISPOSAL FROM VESSEL, the entirety of which is incorporated by referenceherein.

BACKGROUND

Field of Disclosure

The disclosure relates generally to hydrocarbon processing, and moreparticularly, to methods and systems to remove liquids from a vessel.

Description of Related Art

This section is intended to introduce various aspects of the art, whichmay be associated with the present disclosure. This discussion isintended to provide a framework to facilitate a better understanding ofparticular aspects of the present disclosure. Accordingly, it should beunderstood that this section should be read in this light, and notnecessarily as an admission of prior art.

Conventional flare systems used in upstream hydrocarbon processes wherecryogenic or cold hydrocarbon liquids are processed require multipleflares to accommodate wet and dry streams. Due to pressure andtemperature reduction from a high pressure source to a lower pressuresource—a process known as flashing—flared gas streams often containliquids which have been condensed from fluids which have vented,blown-down, or relieved into the flare piping system. The flare pipingsystem, which may be called a flare header, collects all vented,blown-down, or relieved streams and routes these fluid streams throughthe flare header and into a flare knock-out drum. The flare knock-outdrum separates gas from liquids which as described above may havecondensed in the gas stream, and routes the separated gas to a flare forcombustion of any contained hydrocarbons, with the resultant combustionproducts emitted to the atmosphere. The liquids separated in theknock-out drum may collect and require disposal to ensure there is noliquid carryover into the gas stream leaving the flare knockout drum.Such liquid carry-over could cause slugging and unstable flareoperation, excessive heat radiation from combustion, or even snuffingout of the flare flame which would result in not combusting thecontained hydrocarbons.

There are several methods of disposing of such liquids accumulatedwithin a flare knock-out drum. One method is to insert heating coilsinto the system to boil off or vaporize the liquids (if all hydrocarbonwith no water), but the heating coils would require maintenance andadditional operating cost. A pumping system may be used to pump suchliquids to a suitable disposal location. However, the flare knock-outdrum normally operates at a very low pressure and usually does notprovide the suction pressure, known as the net positive suction head orNPSH, for pumping. A typical pumping system therefore requires the flareknock-out drum to be elevated to create the required NPSH. Thiselevation of the flare knock-out drum, the pumps, and the piping,valves, and controls systems for these pumps represent additional cost.

FIG. 1 depicts part of a gas processing system 100 suitable for use withcryogenic liquids. System 100 includes a flare piping system or flareheader 102, which as previously described collects all vented,blown-down, or relieved streams and routes these fluid streams throughthe flare header 102 and into a flare knock-out drum 104. The flareknock-out drum 104 separates gas from liquids and routes the separatedgas to a flare 106 for combustion of any contained hydrocarbons. Theliquids separated in the knock-out drum 104 are sent via a liquidsstream 108 to a blow-case vessel 110. To function properly, theblow-case vessel 110 requires a higher pressure gas stream andassociated piping and valves. Therefore, the liquids stream 108 ispressurized with a dehydrated, higher pressure gas stream, which in FIG.1 may be a defrost gas 112, and then evacuated via a pressure drivingforce to a downstream drum 114 which may contain other liquefiedcondensed hydrocarbons and/or water. The liquids in the downstream drum114 are then disposed via pumping to a suitable destination that isdesigned to handle such fluids. Separated gases in the blow-case vesselmay be sent to another knock-out drum (not shown) for further processingand flaring, or alternatively the separated gases may be returned to thedry flare header using a series of valves and piping 116 configured toreduce the gas pressure to a level suitable for use in the flareknock-out drum 104. The use of the blow-case vessel 110 represents asignificant increase in cost and maintenance because of the amount ofhigh-pressure valves and piping 116 needed to compensate for thedifference between the operating pressures of the flare knock-out drum104 and the blow-case vessel 110. What is needed is a method ofdisposing of the liquids from a flare knock-out drum that reduces theinstallation and maintenance costs of a flare system.

SUMMARY

The present disclosure provides a system for the processing of ahydrocarbon flare gas. An input gas stream contains a gas component anda liquid component. A knock-out drum separates the gas component fromthe liquid component. An eductor has a motive inlet, a suction inlet,and a discharge outlet. The separated liquid component is introducedinto the suction inlet of the eductor. A high-pressure gas stream isintroduced into the motive inlet of the eductor. The high-pressure gasstream has a pressure sufficient to draw the separated liquid componentfrom the knock-out drum and through the discharge outlet.

The present disclosure also provides a cryogenic or cold gas processingsystem. An input gas stream contains a gas component and a liquidcomponent. A knock-out drum separates the gas component from the liquidcomponent. The knock-out drum has a fluid outlet through which theseparated liquid component exits the knock-out drum. A flare flares thegas component of the input gas stream after the liquid component hasbeen separated therefrom in the knock-out drum. An eductor has a motiveinlet, a suction inlet, and a discharge outlet. The separated liquidcomponent is introduced from the fluid outlet to the suction inlet ofthe eductor. A high-pressure gas stream is introduced into the motiveinlet of the eductor. The high-pressure gas stream has a pressuresufficient to draw the separated liquid component from the knock-outdrum and through the discharge outlet.

The foregoing has broadly outlined the features of the presentdisclosure so that the detailed description that follows may be betterunderstood. Additional features will also be described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the disclosure willbecome apparent from the following description, appending claims and theaccompanying drawings, which are briefly described below.

FIG. 1 is a schematic diagram of a gas processing system according toknown principles.

FIG. 2 is a cutaway view of an eductor that may be used with thedisclosed aspects.

FIG. 3 is a schematic diagram of a gas processing system according todisclosed aspects.

FIG. 4 is a schematic diagram of a gas processing system according todisclosed aspects.

It should be noted that the figures are merely examples and nolimitations on the scope of the present disclosure are intended thereby.Further, the figures are generally not drawn to scale, but are draftedfor purposes of convenience and clarity in illustrating various aspectsof the disclosure.

DETAILED DESCRIPTION

To promote an understanding of the principles of the disclosure,reference will now be made to the features illustrated in the drawings.The specific language used herein is not intended to limit the scope ofthe disclosure. Any alterations and further modifications, and anyfurther applications of the principles of the disclosure as describedherein, are contemplated as would normally occur to one skilled in theart to which the disclosure relates. For the sake of clarity, somefeatures not relevant to the present disclosure may not be shown in thedrawings.

At the outset, for ease of reference, certain terms used in thisapplication and their meanings as used in this context are set forth. Tothe extent a term used herein is not defined below, it should be giventhe broadest definition persons in the pertinent art have given thatterm as reflected in at least one printed publication or issued patent.Further, the present techniques are not limited by the usage of theterms shown below, as all equivalents, synonyms, new developments, andterms or techniques that serve the same or a similar purpose areconsidered to be within the scope of the present claims.

As one of ordinary skill would appreciate, different persons may referto the same feature or component by different names. This document doesnot intend to distinguish between components or features that differ inname only. The figures are not necessarily to scale. Certain featuresand components herein may be shown exaggerated in scale or in schematicform and some details of conventional elements may not be shown in theinterest of clarity and conciseness. When referring to the figuresdescribed herein, the same reference numerals may be referenced inmultiple figures for the sake of simplicity. In the followingdescription and in the claims, the terms “including” and “comprising”are used in an open-ended fashion, and thus, should be interpreted tomean “including, but not limited to.”

The articles “the,” “a” and “an” are not necessarily limited to meanonly one, but rather are inclusive and open ended so as to include,optionally, multiple such elements.

As used herein, the terms “approximately,” “about,” “substantially,” andsimilar terms are intended to have a broad meaning in harmony with thecommon and accepted usage by those of ordinary skill in the art to whichthe subject matter of this disclosure pertains. It should be understoodby those of skill in the art who review this disclosure that these termsare intended to allow a description of certain features described andclaimed without restricting the scope of these features to the precisenumeral ranges provided. Accordingly, these terms should be interpretedas indicating that insubstantial or inconsequential modifications oralterations of the subject matter described and are considered to bewithin the scope of the disclosure.

Aspects provided herein are based on replacement of the blow-casesystem, internal heating coils, and/or pumping system of a traditionalcryogenic or cold gas processing system, and instead using an eductorand a motive, higher pressure gas stream to evacuate the liquidscollected within the flare knock-out drum. As shown in FIG. 2, aneductor 200 (commonly called a jet-pump) is a type of pump where theenergy from one fluid is transferred to another fluid via a venturieffect. This principle is based on Bernoulli's law where there is atransfer of kinetic energy to potential energy. As the motive fluid 202passes through a tapered jet nozzle 204, kinetic energy of the motivefluid increases and its pressure is reduced, thereby drawing fluid fromthe suction inlet 206 into the venturi diffuser 208 and through thedischarge outlet 210.

As can be seen, the eductor 200 is a very simple type of device with nomoving parts. FIG. 3 depicts one implementation of the use of an eductorto dispose of liquid from the sump of a flare knock-out drum or othervessel in a cryogenic or cold gas processing system 300. As shown inFIG. 3, system 300 includes a dry flare header 302, which as previouslydescribed collects all vented, blown-down, or relieved streams, androutes these fluid streams through the flare header 302 and into a dryflare knock-out drum 304. The dry flare knock-out drum 304 separates gasfrom liquids and routes the separated gas to a dry flare 306 forcombustion of any contained hydrocarbons. The liquids separated in thedry flare knock-out drum 304 collect in a boot or sump 308, which isconnected to the suction inlet 310 of an eductor 312. Alternatively, nosump or boot is employed in the knock-out drum, and the separatedliquids exit the knock-out drum 304 through a fluid outlet 309. The gasinput to the motive inlet 314 of the eductor 312 is a motive gas, whichin some aspects may be a light hydrocarbon-containing gas stream. Themotive gas may be provided at a pressure of about 100 psig, or at adifferent pressure that is higher than the pressure in the dry flareknock-out drum 304. The pressure within the dry flare knock-out drum 304is just above atmospheric pressure, and may be between 1-2 psig. As withknown liquid disposal practices, a positive pressure is maintainedwithin the dry flare knock-out drum via flare header purge gas toprevent ingress of oxygen from flange leakage when the eductor is beingused. The difference in pressure between the motive gas and the dryflare knock-out drum 304 causes liquid to be drawn from the sump 308,into suction inlet 310, and out of the discharge outlet 316 of theeductor 312 combined with the motive gas. The discharge outlet 316 maybe connected to a dry liquid flare knock-out drum 318, where the liquidsand gases may be separated according to known principles.

FIG. 4 depicts another implementation of the use of an eductor todispose of liquid from the sump of a flare knock-out drum or othervessel in a cryogenic or cold gas processing system 400. As shown inFIG. 4, system 400 includes a dry flare header 402, which as previouslydescribed collects all vented, blown-down, or relieved streams, androutes these fluid streams through the flare header 402 and into a dryflare knock-out drum 404. A defrost gas 405 is introduced into the dryflare knock-out drum 404 to warm up and vaporize light liquefiedpetroleum gas (LPG) liquids. The dry flare knock-out drum 404 separatesgas from liquids and routes the separated gas, including the vaporizedLPG liquids, to a dry flare 406 for combustion of any containedhydrocarbons. The separated liquids exit the dry-flare knock-out drum404 through a fluid outlet 409, which is connected to the suction inlet410 of an eductor 412. The gas input to the motive inlet 414 of theeductor 412 may be a motive gas as shown in FIG. 3, or alternatively maybe a defrost gas. The defrost gas may be provided at a pressure of about100 psig, or at a different pressure that is higher than the pressure inthe dry flare knock-out drum 404. The pressure within the dry flareknock-out drum 404 is just above atmospheric pressure, and may bebetween 1-2 psig. As with known liquid disposal practices, a positivepressure is maintained within the dry flare knock-out drum via flareheader purge gas to prevent ingress of oxygen from flange leakage whenthe eductor is being used. The difference in pressure between thedefrost gas and the dry flare knock-out drum 404 causes liquid to bedrawn through the from the fluid outlet 409, into suction inlet 410, andout of the discharge outlet 416 of the eductor 412 combined with thedefrost gas. The discharge outlet 416 may be connected to a dry liquidflare knock-out drum 418, where the liquids and gases may be separatedaccording to known principles.

The disclosed aspect of using an eductor to evacuate liquids from aflare knock-out drum enables the elimination of a substantial number ofcomponents, as demonstrated by a side-by-side comparison of FIGS. 1 and3. This reduction in components offers the benefits of lower capitalinvestment cost and essentially no maintenance cost when compared to theconventional liquid disposal systems used in the industry currently.

Disclosed aspects may include any combinations of the methods andsystems shown in the following numbered paragraphs. This is not to beconsidered a complete listing of all possible aspects, as any number ofvariations can be envisioned from the description above.

-   1. A system for the processing of a hydrocarbon flare gas,    comprising:    -   an input gas stream containing a gas component and a liquid        component;    -   a knock-out drum that separates the gas component from the        liquid component;    -   an eductor having a motive inlet, a suction inlet, and a        discharge outlet;    -   wherein the separated liquid component is introduced into the        suction inlet of the eductor; and    -   a high-pressure gas stream introduced into the motive inlet of        the eductor, the high-pressure gas stream having a pressure        sufficient to draw the separated liquid component from the        knock-out drum and through the discharge outlet.-   2. The system of paragraph 1, wherein the knock-out drum has a sump,    and wherein the separated liquid component is drawn from the boot or    sump to the suction inlet of the eductor.-   3. The system of paragraph 1 or 2, wherein the high-pressure gas    stream is a defrost gas stream.-   4. The system of any of paragraphs 1-3, wherein the high-pressure    gas stream has a pressure of about 100 psig and the input gas stream    has a pressure between 1-2 psig.-   5. The system of any of paragraphs 1-4, further comprising a dry    flare that flares the gas component of the input gas stream after    the liquid component has been separated therefrom in the knock-out    drum.-   6. A cryogenic or cold gas processing system, comprising:    -   an input gas stream containing a gas component and a liquid        component;    -   a knock-out drum that separates the gas component from the        liquid component, the knock-out drum having a fluid outlet        through which the separated liquid component exits the knock-out        drum;    -   a flare that flares the gas component of the input gas stream        after the liquid component has been separated therefrom in the        knock-out drum;    -   an eductor having a motive inlet, a suction inlet, and a        discharge outlet;    -   wherein the separated liquid component is introduced from the        fluid outlet to the suction inlet of the eductor; and    -   a high-pressure gas stream introduced into the motive inlet of        the eductor, the high-pressure gas stream having a pressure        sufficient to draw the separated liquid component from the        knock-out drum and through the discharge outlet.-   7. The system of paragraph 6, wherein the high-pressure gas stream    is a defrost gas stream.-   8. The system of paragraph 6 or 7, wherein the high-pressure gas    stream has a pressure of about 100 psig and the input gas stream has    a pressure between 1-2 psig.

While the disclosed aspects have been described in connection with theremoval of liquids from a dry flare knock-out drum, it is possible touse the eductor to assist in the removal of liquids from other types ofvessels.

It should be understood that the numerous changes, modifications, andalternatives to the preceding disclosure can be made without departingfrom the scope of the disclosure. The preceding description, therefore,is not meant to limit the scope of the disclosure. Rather, the scope ofthe disclosure is to be determined only by the appended claims and theirequivalents. It is also contemplated that structures and features in thepresent examples can be altered, rearranged, substituted, deleted,duplicated, combined, or added to each other.

What is claimed is:
 1. A system for the processing of a hydrocarbonflare gas, comprising: an input gas stream containing a gas componentand a liquid component; a knock-out drum that separates the gascomponent from the liquid component; an eductor having a motive inlet, asuction inlet, and a discharge outlet; wherein the separated liquidcomponent is introduced into the suction inlet of the eductor; and ahigh-pressure gas stream introduced into the motive inlet of theeductor, the high-pressure gas stream having a pressure sufficient todraw the separated liquid component from the knock-out drum and throughthe discharge outlet.
 2. The system of claim 1, wherein the knock-outdrum has a boot or sump, and wherein the separated liquid component isdrawn from the boot or sump to the suction inlet of the eductor.
 3. Thesystem of claim 1, wherein the high-pressure gas stream is a defrost gasstream.
 4. The system of claim 1, wherein the high-pressure gas streamhas a pressure of about 100 psig and the input gas stream has a pressurebetween 1-2 psig.
 5. The system of claim 1, further comprising a dryflare that flares the gas component of the input gas stream after theliquid component has been separated therefrom in the knock-out drum. 6.A cryogenic or cold gas processing system, comprising: an input gasstream containing a gas component and a liquid component; a knock-outdrum that separates the gas component from the liquid component, theknock-out drum having a fluid outlet through which the separated liquidcomponent exits the knock-out drum; a flare that flares the gascomponent of the input gas stream after the liquid component has beenseparated therefrom in the knock-out drum; an eductor having a motiveinlet, a suction inlet, and a discharge outlet; wherein the separatedliquid component is introduced from the fluid outlet to the suctioninlet of the eductor; and a high-pressure gas stream introduced into themotive inlet of the eductor, the high-pressure gas stream having apressure sufficient to draw the separated liquid component from theknock-out drum and through the discharge outlet.
 7. The system of claim6, wherein the high-pressure gas stream is a defrost gas stream.
 8. Thesystem of claim 6, wherein the high-pressure gas stream has a pressureof about 100 psig and the input gas stream has a pressure between 1-2psig.